Heretofore, there has been known a discharge socket for connecting a drain passage of a toilet main unit of a flush toilet and an underfloor drain pipe, as disclosed in Patent Document 1 (JP 2011-179187A). This discharge socket has: a toilet main unit-side connecting pipe member configured to be connected to an outlet of the drain passage of the toilet main unit; an underfloor-side connecting pipe member configured to be connected to an inlet of the underfloor drain pipe; and an approximately linearly-extending intermediate pipe member connecting the toilet main unit-side connecting pipe member and the underfloor-side connecting pipe member.
In a flush toilet equipped with this discharge socket, when toilet flushing is started to discharge waste in a bowl portion from a toilet main unit, part of flush water stored in the bowl portion firstly flows, as leading flush water flowing on a leading side of the waste, from a drain passage into the discharge socket and then flows toward a building sewer pipe. Subsequently, a flow of flush water flowing mainly on a trailing side of the waste to convey the waste, i.e., a waste conveyance flow, flows into the discharge socket and then flows toward the building sewer pipe together with the waste.